1. Field of the Invention
This invention relates to a spray tip for airless spraying, and, in particular, to such a spray tip provided with a reversible and interchangeable turret member.
2. Brief Statement of the Prior Art
In my prior U.S. Pat. No. 3,831,862, I disclosed a spray tip assembly in which the spray tip orifice is mounted in a removable and reversible sleeve which is secured in the housing with a sliding pin interlock that seats against a spring biased seal. This construction requires loosening of the body from its adapter to reverse and/or replace the spray tip orifice.
In my prior U.S. Pat. No. 4,116,386, I disclosed a spray tip assembly in which the spray tip orifice is mounted in a cylindrical turret member which can be rotated in the housing to reverse the orifice member for cleaning. This construction employs a solid, resilient plastic seal which has a concave, cylindrical sealing surface. U.S. Pat. No. 3,202,360 also discloses an airless spray tip having a rotatable turret member, which is sealed with a packing sleeve and nut.
A recently issued U.S. Pat. No. 4,165,836, discloses that plastic seals experience excessive wear and suggests that an entirely metal seal be used to provide metal-to-metal contact with the turret member. My experience with devices of this invention, however, reveals that a metal seal is not effective with low viscosity liquids, which leak from the assembly under the high pressures used in airless spraying.
In a typical spray application, it is frequently necessary to substitute differently sized orifice members, and this requires interchanging the turret member. Heretofore, the various seals and seal supports dislodged from the spray tips when the turret members were removed, complicating reassembly. It is desirable that the spray tip permit a simple removal and interchanging of the spray orifice without disassembly and without dislodgement of the other parts of the spray tip.
In may prior U.S. Pat. No. 4,484,707 I disclose that difficulties experienced in interchanging turret members can be avoided if the seal is indexed against rotation and retained against dislodgement when the turret member is removed. A similar construction is disclosed in U.S. Pat. No. 4,508,268.
All of the aforementioned patents disclose structures in which the compressive loading on the turret seal is achieved by tightening of the retainer nut which secures the spray tip to the barrel of the spray gun. A wide variety of materials have been suggested for the turret seal, with varying results. U.S. Pat. No. 4,165,836 suggests use of a metal seal. U.S. Pat. No. 4,508,268 suggests the use of hard steel, tungsten carbide, or ceramics. Seals formed of these very hard materials, however, do not seal adequately with low viscosity liquids or with very high liquid pressures.
In my prior U.S. Pat. No. 4,483,481, I have disclosed that the turret member can be sealed effectively against low viscosity liquids without seizure by using a very thin plastic seal on a metal seal support. While a very thin plastic seal such as disclosed in my parent application provides significant improvement over previous seals in that it permits use of the spray tip with low viscosity liquids without leaking and reduces the tendency of the turret member to seize, further improvement, particularly in longevity of the seal is desirable.
It is also desirable to provide a spray tip having a construction which is economical to manufacture and which provides the aforementioned sealing capability and longevity.